The present invention relates to mobile communications devices for use in analog and digital-based cellular communication systems, and, in particular, to a method for conserving power in such mobile communications devices using two receivers for improved diversity reception.
Mobile communications devices or terminals are becoming ubiquitous in modem society. Typical mobile communications devices include pagers, personal digital assistants, mobile phones, and the like, however, all such devices shall be referred to herein as mobile terminals. One of the primary concerns of consumers is directed to the size and weight of the mobile terminals. Many people carry two or more mobile communications devices, such as a pager and mobile phone. If they have to carry a mobile terminal, they want it to be as small and unobtrusive as possible. As a result, there is increasing pressure to shrink the mobile terminal and its internal components.
A second concern exists about the battery capacity of the mobile terminals, and especially the operating time that the battery provides before needing to be recharged. However, this concern is directly at odds with the desire to miniaturize the mobile terminals. Batteries power the myriad of functions available on the mobile terminal and are critical to their operation. While advances have been made in the size and weight of the battery, pressures to make the mobile terminals smaller and lighter have frequently exceeded the ability of the battery designers to produce a battery which supplies the needed power for the desired long interval between recharging while fitting within the condensed mobile terminal.
Therefore, it has become increasingly imperative that the manufacturers of the mobile terminals improve on ways to conserve energy within the mobile terminals. One method to conserve battery power is to put the mobile terminal into a xe2x80x9csleepxe2x80x9d mode. During sleep mode, the mobile terminal is effectively on standby mode waiting for incoming communication. During a sleep period, the receiver in the mobile terminal is not powered so that there is less drain on the battery. A low-power timer in the mobile terminal periodically xe2x80x9cwakes upxe2x80x9d the receiver to process the control channel from the associated base station to determine if there are any incoming messages for the mobile terminal. If not, then the mobile terminal returns to sleep mode. If so, then the mobile terminal remains awake and processes the incoming message according to the instructions of the control channel from the associated base station.
Sleep mode is different from merely powering a mobile terminal off in that sleep mode presupposes waking up periodically to check the control channel. In contrast, turning off may allow for repowering, but it does not presuppose returning to an active state periodically to check the control channel. Two examples of sleeping techniques are seen in U.S. Pat. Nos. 5,224,152 and 5,568,513, which are incorporated by reference.
A third concern is quality of reception. A common problem that occurs in the radio transmission of signals is that the signals are sometimes lost or distorted as a result of multipath fading and interference. One known method of reducing interference and multipath fading is to use a plurality of antennas, and more preferably a plurality of receivers. That is, the mobile terminal includes two receiver circuits, which are then utilized together using interference cancellation or other known performance-enhancing techniques to provide a clear audio signal for the user in the case of a voice call and improved data throughput in the case of a data call. This two receiver methodology is also in direct conflict with both size reduction and battery conservation. The additional circuitry adds a drain on the battery, thereby increasing the frequency of recharging.
With the above concerns in mind, there exists a need in the mobile communications industry to provide a mobile communications device which has the benefits of improved power conservation and the two receiver diversity.
The present invention meets this need by providing a mobile communications device with at least two receivers and a memory. The power consumption of the mobile communications device is controlled by selectively awakening and sleeping the receivers as needed to ensure the desired quality of reception to check the control channel for messages from an associated base station and to handle incoming communications. A plurality of diversity combining techniques are used to improve the performance of the receivers in the mobile communications device. The performance of the receivers is evaluated using the Carrier-to-Interference ratio (C/I), Bit-Error-Ratio (BER), Frame Erasure Rate (FER), Received Signal Strength Indicator (RSSI), soft information confidence, voice quality or a related performance measure or some combination of these performance measurements.
In the preferred embodiment, during periodic waking periods, the mobile communications device checks the individual receivers to see if they can provide adequate reception before relying on both receivers and one of the plurality of diversity combining techniques. The device increments through the diversity combining techniques in order of required power consumption until a desired quality of reception is achieved. Conversely, if reception is adequate, the device checks to see if a lower level of power consumption is possible during the periodic waking periods. This is accomplished by determining whether or not the diversity combining technique can be decremented or scaled back to a single receiver.